DESCRIPTION (Taken directly from the application) The goal of this project is to evaluate the feasibility of in vivo retrovirus mediated gene transfer approaches for the treatment of CF lung disease. Retroviruses have been unpopular for CF gene therapy approaches due to the relatively low titers and low rates of airway epithelial cell proliferation. A recent report suggests that rate of airway epithelial cell proliferation in the lungs of CF patients may be markedly increased due to chronic inflammation. In addition, a number of techniques have been developed to increase airway epithelial cell proliferation in vivo. Significant advances have also been made in the pseudotyping retroviruses that have broadened the host range and enabled generation of markedly increased viral titers. In these studies we will use a pseudotyped retrovirus vector that utilizes the vesicular stomatitis virus G protein for its envelope and can be produced in titers up to > 10 9 CFU per ml. Using this vector which successfully transduces murine airway epithelia in vivo, we will examine the efficiency and efficacy of in vivo gene transfer to freshly excised tracheal explants and animal models including the CFTR (-/-) mouse. We will also attempt to improve the production of VSV-G pseudotyped vectors for in vivo studies. Accordingly, the specific aims of the proposed project are 1) to improve retroviral vectors for in vivo gene transfer, 2) to determine gene transfer efficiency to airway epithelia in vivo, and 3) to correct CF airway epithelia in vivo models and the CFTR (-/-) mouse model.